1. Area of the Invention
The invention relates to the area of information communication and more particularly the processing of binary data structures on their passage through a node of a communication network.
2. Prior art
An ATM (asynchronous transfer mode) layer is used for the transmission of short information packets, known as ATM cells, from a transmission station to a destination station. Known ATM cells are packets of fixed lengths and comprise a header followed by a payload (Jean-Yves Le Boudec in the article "The Asynchronous Transfer Mode: a tutorial" in Computer Networks and ISDN Systems 24 (1992), pages 279-309). The total length of the cells is in each case 53 bytes, the header containing 5 bytes and a payload 48 bytes. Because of the fixed and small size of the cell the cell routing information contained in the header is a tag and not an explicit address. When a switching unit (hereinafter referred to as a node) reads an incoming cell with the route tag m at an input port, it determines an output port j and a tag n from a route switching table. The cell is then written to the output port j and receives the new tag n. The next switching unit extracts corresponding information etc from the new tag n. The route switching tables must be preset or dynamically allocated. The transport of all the cells takes place via one connection.
Translators are also known which can perform the pure header translation in the ATM layer and are additionally able to attach to the ATM cell route information for switching the individual information packets.
In the known ATM systems there is in principle no fixed definition of a data rate, but only the inputting of a maximum data rate on a connecting line. The data rate of a given connection on such a line is defined as the number of cells per unit of time. There is no frame structure on a line of this kind, so that it is not possible to allocate cells to a connection over a fixed time raster. The header data must therefore be newly processed from one cell to another, and it is impossible to predict when the next cell for an existing connection will arrive.
The invention
The object of the invention is substantially to enlarge the possible applications of an ATM system. More particularly, it is an object of the invention to provide the possibility of enabling data to be extracted and inserted on the transmission of information packets through an ATM layer.
To this end, according to the invention, the copy means has an associated first mask for selectively copying all the information sections of the processed data structure, including pre-header and/or tail and/or extra section and payload of the ATM cell, and the insert means has an associated second mask for selectively writing the ATM cell in its payload and header and/or in,at least one of the pre-header, tail or extra sections of the binary data structure.
The method of processing a binary data structure containing an ATM cell on its passage through a node of a communication network is characterised in that
a) a data structure is used which has at least one additional information section in the from of a pre-header and/or tail and/or extra section, the pre-header and/or tail and/or extra section being selectively adjustable (programmable);
b) in that the payload and/or header section of the ATM cell and/or at least one of the pre-header, tail or extra sections is selectively copied via a first mask; and
c) in dependence on the copy operation according to step b) at least one of the information sections consisting of the payload, cell header, pre-header, tail and extra section is selectively written and/or removed via a second mask means.
In the invention, the switching nodes are so constructed that any data can be read selectively bit-wise, byte-wise or even portion-wise via the first mask. Internal or external tables can be addressed with the extracted data. Via the second mask the data structure can again selectively be inserted, added to or erased at any place. Thus even if incorporated in a conventional ATM layer network each node acquires an independent facility to act on content, format and routing. Any desired bits and bytes can be extracted and/or inserted and/or overwritten on the fly. The sources for data for insertion may be not only external tables but also internal or external components, external algorithms, which are implemented, for example, in a form of integrated circuits, and also internal tables and memories. On the other hand, the processing system constructed according to the invention can without difficulty switch ATM cells conventionally, i.e. copy and translate just the header, while all the data in the payload remains untouched.
In a preferred aspect of the invention, the second mask and the associated insert means are provided with means for changing the length of a pre-header and/or of a tail. This includes the possibility of attaching a pre-header and/or tail to an ATM cell. The same applies to an extra addition, the length of which preferably corresponds to the length of the ATM cell with a pre-header and/or tail.
To permit "on the fly" insertion of data into the data structure, in another aspect of the invention, a delay means into which the data structure can be copied undivided is provided in the path between the input interface and the insert means. Preferably, the delay means is provided with means for adjusting the delay.
In this way it is possible to delay inputting the undivided data structure into the insert means until the data for insertion and/or attachment have been extracted from internal and/or external sources and are available for the writing of the data structure passing through.
Each node provided with the system according to the invention is preferably allocated a microprocessor which is coupled to all the processing units of the system and is so constructed that before starting to process the cell stream it selects the input and output interfaces, resets the copy and insert means, sets the first and second masks for selection of the information for copying and insertion and, where applicable, presets the delay time of the delay means.
In a development of the invention, the possible applications can be further enhanced if clock decoupling means are incorporated between the insert means and the output interface.
Other advantageous aspects of the invention are characterised in the subclaims.
The invention is explained in detail hereinafter with reference to examples and the accompanying drawings.